In wireless personal telecommunication, fading causes the fluctuation of reception level and therefore deterioration in the communications. As a method of reducing the fading, a diversity reception has been widely performed. For example if a plurality of antennas are set up keeping predetermined distances from each other, a probability that all the signals from the plural antennas are simultaneously attenuated is little, and hence a high reliability is assured. Signal to Interference margins can be increased by as much as 10 dB when two antennas are used rather than one. Various kinds of diversity reception methods are known. U.S. Pat. Nos. 4,696,058, issued Sep. 22, 1987 (Tachita et al), and 4,977,616 issued Dec. 11, 1990 (Linder et al), for example, teach diversity receivers which use two or more antennas and one receiver circuit. An antenna selection circuit switches to any one of the antennas in response to received signal strength indication generated by the receiver. In U.S. Pat. No. 5,097,484, issued Mar. 17, 1992 (Akaiwa), on the other hand, discloses a system which uses two antennas and two receivers.
In the wireless personal telecommunication environment, it is normally the cordless fixed part (often called base station) that performs antenna diversity reception because it is more difficult to provide more than one antenna in the cordless portable part (often called microcellular phone, handset or such name). In one system such as one taught in the above-referenced U.S. Pat. No. 5,097,484, a link from the base station to a handset is carried out at one frequency and a link in the opposite direction is at a different frequency. In the digital communication environment, it is also possible to use a duplexer which permits a two-way communication on a single frequency. U.S. Pat. No. 5,067,173, issued Nov. 19, 1991 (Gordon et al) describes such an arrangement.
In most cases, if "perfect" diversity is assumed, a system requires apriori knowledge of the received signal strength indication (RSSI for short) at all antennas which can be selected. Such information can only be achieved through the use of dual receivers. In such an arrangement, the RSSI of the signal received on each antenna is continuously monitored, and the best antenna is always selected. This implementation adds considerable cost to a radio receiver. However, without a dual receiver, the unused antenna must be sampled periodically, resulting in bit hits (lost or corrupted bits) or frame hits (lost or corrupted TDD frame) in the received data whenever the "tested" antennas has a very poor RSSI.
It is therefore desirable to implement antenna diversity while only using a single receiver, and at the same time minimize the effect of bit hits due to antenna switching.